In known pressurized water reactors (PWR) and boiling water reactors (BWR), a reactor core may contain a large number of fuel rods that are several meters in height. The reactor core may be surrounded by water contained within a reactor vessel. Additionally, the reactor may contain in-core instrumentation including a number of instrument assemblies located in the reactor core.
During maintenance or refueling operations, in which some or all of the fuel rods in the reactor core may be inspected or replaced, respectively, the reactor vessel must be at least partially disassembled or removed in order to gain access to the reactor core. Prior to disassembling the reactor vessel, the in-core instrumentation may be disconnected and physically removed from the reactor core by opening the reactor vessel penetrations and pulling the in-core instrumentation out of the reactor core. However, in order to remove the in-core instrumentation, an operator and/or tool is typically introduced into the containment vessel in order to access the in-core instrumentation. For example, the containment structure may comprise a man-way that is large enough for an operator to enter a containment region located above the reactor pressure vessel.
Work conditions and precautionary measures may be established to allow operators to position themselves on top of the reactor pressure vessel head to withdraw the in-core instruments. To withdraw an instrument, the operator may loosen a Swagelok fitting for each in-core instrument and physically grasp the external end of the in-core instrument, which may comprise a forty to eighty foot long tube or cable. The operator then pulls about fifteen feet of the in-core instrument through the reactor pressure vessel such that the lower end of the in-core instrument is withdrawn from the reactor core.
Withdrawing the in-core instrumentation via known refueling operations may therefore not only require providing access to the inside of containment, but the refueling tool or operator may also need to be placed in close physical proximity to the reactor core in order to loosen or open the Swagelok fitting located on top of the reactor pressure vessel. Accordingly, two of the primary means of reducing potential radiation exposure, namely providing shielding from and maintaining distance to a radioactive source, may be compromised in known refueling operations. Alternatively, if the in-core instrumentation and reactor core are first allowed to cool down and/or become less radioactive before the operator or tool is used, then a significant amount of time may transpire in which the reactor module is taken off-line and is unable to generate electricity.
This application addresses these and other problems.